The present device and method provides a significant departure from straight screws for fixation of bone or other solid material.
Traditional screws are basically solid devices with a head that articulates with a screwdriver, a straight shaft, and a tip. The shaft may be fully threaded or only partially threaded; a portion of the tip may be threaded and may or may not have a self drilling or self tapping design. In addition, the head of the screw itself may have threads that articulate with a metal plate to assist the screw in locking to the plate.
The clinical success of plate and screw systems for internal fixation of fractures is well documented. When used in conjunction with a bone plate, a conventional screw would enter into a smooth aperture in the plate and is then driven into the bone. The head of the screw would then apply a downward pressure on the plate, assuming the head of the screw is larger than the aperture in the plate.
Recent advances in the field of orthopedic fracture fixation have led to the development of “locking” plates. In the locking configuration the screw head itself is threaded. The corresponding aperture in the plate is compatibly threaded. When the screw has been driven sufficiently into the bone, the head of the screw can engage the corresponding threads on the plate and create a locked assembly, thus providing a desirable mechanical advantage over conventional plating systems.
Screws are frequently used by themselves in bone fracture and reconstructive procedures. There are many bones in the human skeleton that are constituted largely of cancellous “spongy” bone. Often, these bones are best fixed with a screw that can be entirely buried into the substance of the bone without leaving any component of the screw outside to minimize irritating adjacent tissues, or to avoid scouring the cartilage of a joint. In such cases, it is desirable that the head of the screw itself has threads designed to engage bone, i.e. “bone threads.”
Another option for fixation of cancellous bone fractures is, what is referred to by those skilled in the art, as a “headless screw.” As the name implies, a headless screw has no distinctive head. The screw driver engages the screw at the terminus away from the tip or leading end of the screw. The scaphoid bone in the wrist is often fixed with such headless screws, or screws that can be buried entirely into the bone. Presently, there are several known screws in the art designed for use with scaphoid bones and other similar bones. For example, the Herbert screw (U.S. Pat. No. 4,175,555, issued to Herbert); the Accutract screw from Acumed (U.S. Pat. Nos. 5,562,672 and 5,964,768, issued to Huebner); the TwinFix screw from Stryker-Leibinger; the Kompressor screw from KMI; and the SLIC screw system from Acumed.
All of these screws are straight, except for the SLIC screw, which is articulated at the waist. Most existing screws also have a cannulated version for increased accuracy of insertion. A smooth pin can also act as a guide by first inserting the pin into the bone under radiographic control.
The scaphoid bone has an elongated curved shape that makes it difficult to fix with a straight screw. Frequently, the screw is placed in a suboptimal position and fails to engage and hold the fractured bone segments. The challenge in scaphoid fracture fixation is placing a straight screw into a curved bone. Failure to achieve accurate placement of the screw into the bone can lead to failure of fracture healing.
It is therefore an object of the present invention to improve bone fracture fixation and facilitate placement of a bone screw. It is a further object of the present invention to provide a curved screw that can follow the natural curvature of any skeletal bone, especially fractured joints such as found in the shoulders, wrists, and equivalents thereof. It is another object of the present an invention to provide a curved apparatus that operates in conjunction with a curved screw as well as a curved drill bit capable of various lengths and curvatures. It is a further object of the present invention to provide a curved screw capable of compressively attaching to a bone plate. It is a further object of the present invention to provide a curved drill bit and curved screw that can be used in conjunction to facilitate reattachment of fractured bone segments.